This invention relates to antenna systems and, more particularly, to antenna systems for use in military defense missiles. The function of these missiles is to detect, locate, and destroy enemy targets.
To enhance the missile's effectiveness, it is often desirable to have operational capability in both active and passive modes. In the passive mode, the antenna simply "listens" for any signals which may be radiated by the target. This operation is best performed by a low gain wide band antenna. Conversely, in the active mode the antenna transmits signals which are reflected by the target and subsequently received by the same antenna. This operation is best performed by a high gain narrow band antenna.
An "all-passive" antenna system which provides both wide and narrow beam capabilities (for initial target acquisition and subsequent high accuracy tracking) is described in U.S. Pat. No. 4,095,230, issued June 13, 1978 to the present applicant. The present invention is a variation of the apparatus there described. Basically, that apparatus included a low gain, wide band antenna which also functioned as a reflector for the high gain, narrow beam antenna system. By comparison, in the present invention, the low gain wide band antenna performs no signal reflection function. Instead, that function is performed by a frequency sensitive parabolic dish which lies between the low gain, wide band antenna and a waveguide feed. The waveguide-fed reflector antenna allows the use of a high power transmitter, which results in extended range tracking capability.
This dish is substantially transmissive for frequencies at which the low gain wide band antenna system operates; and is substantially reflective for frequencies at which the high gain narrow band antenna operates. Thus, in operation, initial target detection is performed by receiving signals with the low gain, wide band antenna which have passed through the parabolic array, and the subsequent terminal mode tracking of the target is achieved by transmitting and receiving signals that are reflected by the array.